For most people, no. In large trials of adults without known heart disease, low-dose omega-3 capsules did not lower the rate of heart attacks, strokes and cardiovascular deaths. Fish oil supplements are not a proven way to prevent a first heart event.
The picture is different, and still debated, for one prescription medicine made of purified EPA, one of the two main omega-3 fats in fish. In one trial it lowered events in high-risk people with raised triglycerides who were already taking statins. A second trial of a different prescription omega-3 found no benefit at all. Both results belong in an honest answer.
Key takeaways
- A low-dose omega-3 capsule did not reduce major heart events in a trial of nearly 26,000 adults without heart disease.
- Purified prescription EPA reduced events in one trial of statin-treated, high-risk patients, while a prescription EPA and DHA product showed nothing in another.
- Pooled trial data tie omega-3 capsules to more atrial fibrillation, especially at higher doses.
- Store-bought fish oil is not the product tested in the positive trial, so that result does not carry over to it.
- Talk with your prescriber before you start, stop or change any omega-3 product or medication.
What omega-3 fats do in the blood
EPA and DHA are the omega-3 fats found in oily fish. In prescription strength they lower triglycerides, a blood fat covered in our guide to triglycerides and heart risk.
They do not lower LDL cholesterol. In a four-week trial that compared six supplements with placebo and a low-dose statin, fish oil did not lower LDL cholesterol any more than placebo did.1
A better blood number is not the same thing as fewer heart attacks. That question can only be answered by outcome trials, which follow thousands of people for years and count events.
Three large trials, side by side
| Trial and product | Who was studied | Main result |
|---|---|---|
| VITAL: low-dose omega-3 capsule | 25,871 US adults without heart disease (men 50 and older, women 55 and older) | No significant drop in major cardiovascular events |
| REDUCE-IT: high-dose purified EPA, prescription | 8,179 people on statins with raised triglycerides, plus heart disease or diabetes with other risk factors | Fewer events than placebo |
| STRENGTH: high-dose EPA plus DHA, prescription | 13,078 people on statins at high risk, with high triglycerides and low HDL | No difference, trial stopped early |
What the prevention trial found
VITAL tested the question most supplement users care about: does a daily omega-3 capsule protect people who do not have heart disease?
Over a median of 5.3 years, a major cardiovascular event occurred in 386 people taking omega-3 and 419 taking placebo, a difference that was not statistically significant.2 Heart attacks counted alone were less common in the omega-3 group. That was a secondary result, though, and secondary results are leads to test, not proof.
Why REDUCE-IT and STRENGTH disagree
In REDUCE-IT, the main endpoint occurred in 17.2% of people taking purified EPA and 22.0% of people taking placebo over a median of 4.9 years.3 Deaths from cardiovascular causes were lower too.
STRENGTH was halted early because a benefit looked unlikely: the main endpoint occurred in 12.0% of the omega-3 group and 12.2% of the corn oil group.4
Nobody has settled why two similar trials came out so differently. Two explanations are discussed most:
- The product. REDUCE-IT used EPA alone. STRENGTH used EPA combined with DHA.
- The placebo. REDUCE-IT used mineral oil as its comparison. STRENGTH used corn oil.
A later analysis of REDUCE-IT blood samples found that markers of inflammation rose in the mineral oil group and barely changed in the EPA group, and its authors called the effect on the trial result uncertain.5 A fair reading is that the benefit of purified EPA in that specific group may be real, but its true size is disputed.
The atrial fibrillation signal
Omega-3 capsules are not free of risk. A pooled analysis of seven outcome trials with 81,210 participants linked omega-3 capsules to a 25% higher relative risk of atrial fibrillation, with a larger increase in the trials that used higher doses.6
REDUCE-IT showed the same pattern: 3.1% of the EPA group were hospitalized for atrial fibrillation or flutter, compared with 2.1% on placebo. Serious bleeding was slightly more common with EPA, a difference that did not reach statistical significance. In STRENGTH, stomach and bowel side effects were more frequent with omega-3 than with corn oil.
If you have had atrial fibrillation, or you take a blood thinner, bring that up before you take any omega-3 product.
Prescription EPA and store-bought fish oil are not the same
The one positive trial tested a purified, high-dose prescription medicine in people who already had high risk, raised triglycerides and a statin. It did not test the fish oil sold in stores, and it did not test people at ordinary risk.
Supplements are not reviewed and approved the way prescription medicines are, and the trial of a low-dose capsule in the general population was neutral. So REDUCE-IT is not a reason to buy fish oil.
Eating fish as part of an overall eating pattern is a separate question. See our guide to the best diet for heart health.
Do not start, stop or change a medication, including a prescription omega-3, without your prescriber. Tell them about any supplement you take.
Next step: find out what is driving your risk
Whether omega-3 treatment is even worth discussing depends on your own numbers and history. Both Cardio Res-Q assessments, the Comprehensive Assessment ($775) and the Enhanced Assessment ($999), include ApoB, Lp(a), hs-CRP, insulin, glucose and A1c, along with a clinical evaluation. The Cleveland HeartLab panel also reports oxidized LDL and small dense LDL, plus other proprietary markers.
The personalized plan may include supplement recommendations. It is reasonable to ask what evidence supports any of them for you. If you are already treated, read Already on a Statin? first, then see the Cardio Res-Q program page.
Are You a Candidate for Cardio Res-Q?
Three quick questions about the risk factors we screen for. Your answers stay between you and the clinic.
Frequently asked questions
Should I take fish oil to prevent a heart attack?
The largest trial in people without heart disease did not find that a daily omega-3 capsule lowered major cardiovascular events. That is why fish oil supplements are not considered a proven prevention tool. Whether any omega-3 product makes sense for you is a decision to make with your clinician.
Is prescription omega-3 the same as a fish oil supplement?
No. The prescription product in the positive trial was purified EPA given at high dose to statin-treated patients with raised triglycerides and high risk. Supplements vary in what they contain and were not what that trial tested.
Can fish oil cause atrial fibrillation?
Trials suggest it can raise the chance. Pooled data from large outcome trials show more atrial fibrillation in people taking omega-3 capsules than in people taking placebo, and the increase looked larger at higher doses. Most people in those trials did not develop it.
Does fish oil lower cholesterol?
It lowers triglycerides when given in prescription strength, but it does not lower LDL cholesterol. In a head-to-head trial, fish oil had no more effect on LDL than placebo.
Related reading
This article is for general education and is not medical advice. Decisions about testing and medication should be made with your clinician. If you have chest pain or other symptoms of a heart attack, call 911.
